This invention is directed to an improved dispersion for bonding together man-made fibers such as crimped textile tows to be formed into nonwoven articles, such as tobacco smoke filter rods, which rods, after use as filter elements on cigarrets, will disintegrate into individual fibers upon prolonged contact with water or moisture in the environment; and to tobacco smoke filter rods of man-made fibers bonded with such improved dispersion.
Tobacco smoke filter rods made from cellulose acetate fibers are well-known and have been described in a number of patents. U.S. Pat. Nos. 2,794,239 and 3,017,309 are but two such patents from the many which describe filters of this type.
The use of bonding plasticizers to obtain more rigid tobacco smoke filter rods for the purpose, for example, of eliminating the collapse of the filter rod when it becomes moist during smoking is also well-known. For instance, U.S. Pat. Nos. 3,003,504, 3,008,474 and 3,229,699 disclose plasticizers for such purpose.
Bonding plasticizers of the prior art may be prepared from esters of glycerin or esters of triethylene glycol. Such plasticizers are externally applied in relatively small quantities to a mass of individual filaments. The surface of the filaments, wherever plasticizer is present, quickly becomes soft and "sticky" due to the mild solvent action of the plasticizer. At the points where individual filaments touch each other, the softened surfaces merge together in a homogeneous mass. This phenomenon occurs in the first few minutes after the plasticizer has been applied. As time passes, the plasticizer migrates deeper into the filaments, the surface concentration becomes less and less, and the surface begins to harden or "cure." The surface is no longer soft and tacky, but has returned essentially to its original consistency. At those places where filaments contact each other, a strong, solid "weld" has taken place. These welded intersections hold each filament firmly in position relative to adjacent filaments, and an overall rigid structure results. The more rigid internal structure results in the filter rods produced from the tow, and facilitates further processing of the rods into tips or filter elements for attachment to cigarettes.
Cellulose acetate fibers bonded with plasticizers of the prior art such as triacetate of glycerol have a disadvantage from the standpoint of subsequent disposal after use in that the bond is permanent. Filters prepared with this plasticizer and a number of other bonding plasticizers remain firmly bonded together even after being buried in the ground for 1 year and exposed to about 40 inches of rainfall.
Filter cigarette butts are discarded in public places where they are unsightly. They are also discarded in public and private sewage systems where they may block screens and/or pipes in the systems. These two problems may be alleviated if not overcome when the fibers in the filters are not bonded permanently together.